Generally, commutator motors with brushes are frequently used as an electric motor mounted on an automobile. This electric motor has a cylindrical yoke, a plurality of permanent magnets arranged on the inner circumferential surface of this yoke, and an armature arranged inside these permanent magnets and rotatable with respect to the yoke. This armature has a rotary shaft, and an armature core which is fixed onto this shaft and has a plurality of radially formed teeth, and a coil wound around the teeth. The coil has a plurality of winding wires wound around the teeth through slots formed between the teeth. The respective winding wires are connected to a plurality of segments of the commutator fixed to the rotary shaft.
The commutator has a plurality of segments which is formed from metal pieces, is insulated from each other and disposed in a columnar shape. A winding starting end and a winding finishing end of the winding wire are connected to each of the segments. Additionally, a plurality of brushes is connected to the segments of the commutator so as to be capable of making sliding contact therewith, and an electric current is supplied to the coil via these brushes. Also, a magnetic field is formed in the teeth of the armature core due to an electric current which flows through the coil, and the armature is rotated with the rotary shaft by a magnetic attractive force or repulsive force which is generated between the teeth and the permanent magnets fixed onto the yoke.
In this electric motor, there is a motor including a total of three brushes, a brush for low speed and a brush for high speed which are selectively connected to a positive terminal of a power source and a common brush connected to a negative terminal of the power source. By selectively connecting either the brush for low speed or the brush for high speed to the positive terminal, the rotational speed of the armature provided in the electric motor can be changed (for example, PTL 1).
FIG. 17 is a developed view of an electric motor 80 with four poles, sixteen slots, and sixteen segments, having four permanent magnets (two pole pairs), sixteen teeth (slots), and sixteen segments, which is disclosed in PTL 1. As for the permanent magnets 81, N poles and S poles are arranged alternately. The slots 83 are gaps between the teeth 82 adjacent to each other. As shown in this drawing, No. 1 to No. 16 are given to the respective teeth 82 and the respective segments 84.
A winding wire 87 and a winding wire 88, which is arranged at a position which is point symmetric with respect to the winding wire 87, are substantially simultaneously wound around the teeth 82 by a double flyer. The winding wire 87 is split into two coil winding wires 93A and 93B, and is wound around the teeth 82 with different numbers. That is, the winding wire 87 connected to a No. 2 segment 84e passes through a slot 83e between a No. 16 tooth 82 and a No. 1 tooth 82, passes through a slot 83f between a No. 3 tooth 82 and a No. 4 tooth 82, and is wound in a forward direction around No. 1, No. 2, and No. 3 teeth 82 n times (n is a natural number), whereby a coil winding wire 93A is formed.
Next, the winding wire 87 passes through a slot 83g between a No. 7 tooth 82 and a No. 8 tooth 82, passes through a slot 83b between a No. 4 tooth 82 and a No. 5 tooth 82, is wound in an opposite direction around No. 5, No. 6, and No. 7 teeth 82 n times, and is connected to a No. 3 segment 84a, whereby a coil winding wire 93B is formed. The slot 83g exists at a position deviated in a circumferential direction from the slot 83f by a mechanical angle of 90°, and the slot 83b exists at a position deviated in a circumferential direction from the slot 83e by a mechanical angle of 90°.
On the other hand, the winding wire 88 is split into two coil winding wires 93C and 93D, and is wound around the teeth 82 with different numbers. That is, the winding wire 88 connected to a No. 10 segment 84b passes through a slot 83h between a No. 8 tooth 82 and a No. 9 tooth 82, passes through a slot 83i between a No. 11 tooth 82 and a No. 12 tooth 82, and is wound in a forward direction around No. 9, No. 10, and No. 11 teeth 82 n times (n is a natural number), whereby a coil winding wire 93C is formed.
Next, the winding wire 88 passes through a slot 83j between a No. 15 tooth 82 and a No. 16 tooth 82, passes through a slot 83d between No. 12 and No. 13 teeth 82, is wound in an opposite direction around No. 13, No. 14, and No. 15 teeth 82 n times, and is connected to a No. 11 segment 84c, whereby a coil winding wire 93D is formed. The slot 83j exists at a position deviated in a circumferential direction from the slot 83i by a mechanical angle of 90°, and the slot 83d exists at a position deviated in a circumferential direction from the slot 83h by a mechanical angle of 90°.
In the electric motor 80, the winding wire 87 and the winding wire 88 which are wound in this way are wound 8 times while the segment 84 of winding starting is shifted sequentially one by one in the forward direction, and an armature coil is formed by the winding wire 87 and the winding wire 88.
The No. 2 segment 84e and the No. 10 segment 84b, as well as the No. 3 segment 84a and the No. 11 segment 84c are short-circuited by connecting wires 90. Additionally, the brushes 91 which come into sliding contact with the segments 84 includes three brushes of a brush 92a for low speed and a brush 92b for high speed which are selectively connected to a positive electrode terminal of a power source, and a common brush 92c connected to a negative electrode terminal of the power source. The brush 92a for low speed and the common brush 92c are arranged at an interval of 180° in electric angle.
The brush 92b for high speed is arranged in the state of being separated by a predetermined angle in the circumferential direction from the brush 92a for low speed. Also, when an electric current is supplied to between the brush 92a for low speed and the common brush 92c from the power source, the electric motor 80 is rotationally driven at a low speed, and when an electric current is supplied to between the brush 92b for high speed and the common brush 92c from the power source, the electric motor 80 is rotationally driven at high speed. Since the No. 2 segment 84e and the No. 10 segment 84b, as well as the No. 3 segment 84a and the No. 11 segment 84c are short-circuited by the connecting wires 90 so as to have the same potential, even in the electric motor 80 with four magnetic poles, low-speed rotational driving and high-speed rotation of the electric motor 80 are possible due to the three brushes 92a, 92b, and 92c. 
Here, the winding wire 87 and the winding wire 88 of the electric motor 80 adopt a configuration using coil winding wires split in two. The reason is as follows. In a case where the winding wire 87 and the winding wire 88 are split, the number of times of winding a coil winding wire can be distributed into two (n and n). However, in a case where the winding wires are not split, the number of times of winding the coil winding wire 93A becomes 2n in the winding wire 87, and similarly the number of times of winding the coil winding wire 93C becomes 2n in the winding wire 88.
In this case, for example, there is an increase in the number of crossovers 94A of the coil winding wire 93A which crosses over from the slot 83e to the slot 83f, and the number of crossovers 94C of the coil winding wire 93C which crosses over from the slot 83h to the slot 83i. Therefore, in the armature coil formed by overlapped winding, in a case where the coil winding wires 93A and the 93C are wound so as to overlap the outside of the coil winding wires 93A and 93C which are already wound, winding thickening occurs, so that axial dimensions of the armature becomes large and the space factor of the winding wires decreases.
Thus, the configuration of coil winding wires split into two is adopted to reduce the axial dimensions of the armature and improve the space factor of the winding wires. Moreover, as described above, in the multi-pole electric motor with four or more poles, it is useful to adopt the structure in which the connecting wires are arranged at the armature and the configuration of split coil winding wires, in order to allow the rotational speed of the armature to be changed by three brushes and to achieve reduction in the axial dimensions of the armature and improvement in the space factor of the winding wires.